Abstract
A polyphasic approach was applied to describe a colony-forming Desmodesmus species collected from the Nile River, Maadi area, Helwan district, Egypt. The isolate grows best at moderate temperature and relatively high light intensity. The phenotypic features revealed the presence of both unicellular and colonial forms of the isolate and the latter form was either 2-4 celled. Cells were 4-6 mu m +/- 0.5 at their widest point and 11-15 mu m +/- 0.48 in their length with spiny projections that encircled the cells. Cells were heavily-granulated and enclosed within common mucilaginous sheath. Colonial forms were developed through production of daughter cells within mother cell. Molecular analysis using 18S rRNA gene showed some similarity to its nearest relative (Desmodesmus communis) whereas the phylogenetic analyses clustered it together with other Desmodesmus spp. and away from Scenedesmus spp. from the database. However, the use of ITS-2 as a phylotaxonomic marker proved to be more resolving and confirmed the generic identity of the isolate as Desmodesmus spp. The fatty acid composition revealed the presence of saturated palmitic fatty acid as the most abundant component followed by monounsaturated palmitoleic acid whereas the polyunsaturated fatty acids were in relatively low abundance. The palmitoleic acid in particular is suggested to be involved in active defense mechanism. The phytochemical screening revealed the presence of alkaloids and saponins and absence of tannins. Fractions of methanolic extracts showed antimicrobial activities against pathogenic bacterial strains including multi-drug resistant ones. This study documents the presence of this strain in the River Nile and highlights its biotechnological potential as a source of bioactive compounds.